Multi-state photoconductive logic circuits



Nov. 17, 1964 R. H. TERLET 3,157,791

MULTI-STATE PHOTOCONDUCTIVE LOGIC CIRCUITS Filed July 27, 1961 2 Sheets-Sheet 1 48 44 49 4s 14 l 16 L 54\ 4 52 60 56 34 i 62 58 SET 66 OUTPUT A 1 52 7 26 42 OUTPUT TRIGGER 24 68 INVENTOR H 70 REN H TERLET ATTORNE United States Patent 3,157,791 MUL'Il-STATIE PHQTU CGNDU'CTEVE LUGZIC tJlRiJiT Rene H. Terlet, Ussining, NY assignor to International Business Machines (Ierporation, New York, N.Y., a corporation of New York Filed July 2'7, 196i, Ser. No. 127,301 r '7 Claims. (Ql. ESQ-@239) This invention relates to circuits which are capable of achieving more than one stable state, and more particularly to circuits of this description which operate on photologic principles.

One object of the present invention is to provide improved photologic flip-flop or trigger circuits.

Another object of the present invention is to provide such bi-stable circuits which are characterized by very reliable operation and which may be very simply controlled to set to a new state, to reset to the previous state, or to trigger to the opposite state, whichever that state may be.

Another object of the present invention is to provide an improved photologic ring or counter circuit which is characterized by very positive and trouble-free operation.

Another object of the present invention is to provide a photologic ring circuit which is very easily and simply controlled for shifting operation in either of two selected directions.

In carrying out the above objects of this invention in one preferred embodiment thereof, there is employed a main voltage responsive light source for each state to which the circuit is to be switched with a conditioning voltage responsive light source associated with each main.

light source. Each of the light sources have a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when once illuminated. And each main light source has photoconductors arranged to receive illumination therefrom including a shut-ofi photoconductor connected in shunt with the associated conditioning light source and a pickup photoconductor connected to supply a pick-up voltage to the conditioning light source for the next succeeding main light source to be actuated. Switching means is provided which is operable to turn ofr any illuminated main light source whenever a shift in state is required, together with circuit means including a condition photoconductor associated with each conditioning light source for turning on the next main light source to be actuated.

Further objects and advantages of the present invention will be apparent from the following description and the accompanying drawings as follows:

FIG. 1 is a schematic circuit diagram of a photologic flip-flop or bi-stable circuit in accordance with the present invention.

And FIG. 2 is a schematic circuit diagram of a reversible ring circuit in accordance with the present invention.

Referring more particularly to FIG. 1 there is shown a bi-stable embodiment of the present invention including main voltage responsive light sources Iii and 12 for the two different stable states. Respectively associated with the main light sources and 12 are conditioning light sources 14 and 16. When the circuit is in one stable state as signified by the illumination of light source 12, an output A is produced at terminal 18. When the circuit is in the other stable state, signified by the illumination of lamp Id, an output B is produced at terminal 2b. In order to place the circuit in the first stable state, the circuit may be set by the illumination of an input lamp 22. In order to place the circuit in the other stable state to produce an output B, the circuit may be reset by illumination of input lamp 24. And in order to change the SAS'ZJZJE Patented Nov. 17, 1954i ice state from whatever state it happens to be in, to the other stable state, an input may be provided by illuminating a trigger input lamp 26.

Switching and control functions are accomplished in response to illumination of the various lamps by means of photoconductors. For instance, a photoconductor 28 is provided to be illuminated by main lamp l2 and connected to provide output A at connection 18, and a photoconductor 30 is arranged to receive illumination from main lamp i0 and connected to provide output B on connection 2t Throughout the drawings, the rectangular symbols such as are used for photoconductors 28 and 30 signify devices which have photoresponsive properties which are commonly referred to as photoconductors. Since these devices have a lowered impedance when illuminated, they are more accurately described as photoresponsive impedances, but the popular photoconductor term is used in this specification. The preferred photoconductor devices will be described more fully below. Throughout the drawings the convention is followed that each phctoconductor device is illuminated only by the first lamp positioned to the left of that photoconductor. Thus, photoconductor 30 is illuminated only by lamp 10 and is not illuminated by lamp 12.

In order to simplify the drawings, whenever a common ground connection is called for the conventional ground symbol is employed, and whenever a power connection is required, it is indicated by a small circular terminal and a plus sign. It will be understood that a conventional source of power (not shown) may be employed.

In FIG. 1, the main lamps 10 and 12 are respectively provided with latching photoconductors 32 and 34 which are connected for energization from a power terminal 36 through a resistor 38 and a common latching power bus 49. The bus 40 may be lowered to substantially ground potential by means of a photcconductor 42 whenever the trigger lamp 26 is illuminated. This is effective to drop out the latching of whichever one of the lamps 10 or 12 is latched in the illuminated position at the time. This operation will be described more fully below.

Conditioning light sources 14 and 16 are also provided with latching photoconductors respectively indicated at 44 and 46. The conditioning lamps 14 and 16 also include condition photoconductors associated therewith and respectively indicated at 48 and 49. Each condition photoconductor is arranged to supply power to illuminate the associated main lamp whenever the associated conditioning lamp is illuminated with the concurrent energization of the condition photoconductor power supply circuit indicated at 5% Circuit 50 supplies power to both of the condition photoconductors 48 and 49 through a resistor 51. A pho-toconductor 52 is connected to circuit 50 and arranged for illumination by trigger lamp 26 to reduce the potential of circuit 50 to essentially ground level when trigger lamp 26 is illuminated. The purpose for this arrangement will be described more fully below.

The main lamps 10 and 12 each have a grounding photoconductor associated therewith for grounding out the associated conditioning lamp. Thus, main lamp 10 has a grounding photoconductor 53 which is connected in shunt with conditioning lamp 14 to extinguish that lamp when lamp I0 is illuminated. This photoconductor 53 is sometimes referred to below as a shut-off photoconductor. And photoconductor 54 is arranged for illumination by main lamp 12 and connected in shunt with conditioning lamp 16 to extinguish that lamp whenever main lamp 112 is illuminated. Also, each main lamp has associated therewith a photoconductor which is connected in shunt with the other main lamp. Thus, photoconductor 56 is arranged to receive illumination from lamp lit and connected in shunt with lamp 12 while photoconductor .3 58 is arranged to receive illumination from lamp 12 and connected in shunt with lamp 1%. Photoconductors 56 and 58 may be referred to below as hold-oil photoconductors for reasons which will be apparent when the operation of the system is described.

Each main light source also has associated therewith a pick-up photoconductor which is connected and arranged to energize the conditioning light source associated with the next main light source to be illuminated. Thus, there is a pick-up photoconductor 60 associated with main light source which is connected to supply power to conditioning light source 16, and there is a pick-up photoconductor 62 associated with main light source 12 connected to supply pick-up power to the conditioninglight source 14.

In order to initiate operation of the system of FIG. 1 either the set lamp 22 or the reset lamp 24 is illuminated. Associated with the set lamp 22 there is a photoconductor 64 connected to supply power to main lamp 12, and another photoconductor 66 connected in shunt with lamp 10. Thus, if set lamp 22 is illuminated, the circuit supplied by photoconductor 64 causes illumination of main lamp 12 and photoconductor 66 causes main lamp 10 to be extinguished. Similar photoconductor circuits are associated with reset lamp 24. Thus, photoconductor 68 is connected to supply power to main lamp 19, and photoconductor 70 is connected in shunt with main lamp 12 so that illumination of reset lamp 224 causes main lamp it) to be picked up, and main lamp 112 to be extinguished.

The operation of the system of FIG. 1 is as follows: Assume that the set lamp 22 has received an illuminating pulse of voltage so as to cause the illumination of main lamp 12. Lamp 12 is then latched on through its latching photoconductor 34 and the circuit 40. Through photoconductor 54, which is conncted in shunt with conditioning lamp 16, the illumination of lamp 112 assures that conditioning lamp 16 will remain dark. The illumination of pick-up photoconductor 62 by lamp 12 connects power to pick-up conditioning lamp 14 which then latches on through the associated latching photoconductor 44. The condition photoconductor 43 then supplies a voltage to main lamp 10 from circuit 59. However, the shunt photoconductor 58, which is illuminated by main lamp 12, maintains the voltage across main lamp 10 at a low value below that necessary to cause illumination. Thus, main lamp 12 is illuminated, and conditioning lamp 14 is illuminated, and lamps 1t) and 16 are not illuminated. The illumination of photoconductor 28 by main lamp 12 provides an output A at connection 13. The condition of the circuit thus remains stable until another input signal is received.

If an input is received at the trigger lamp 26 so as to illuminate photoconductor 42, then the main lamp latching circuit is reduced in voltage to such a point that main lamp 12 is extinguished. This does not extinguish conditioning lamp 14 because it is latched in the energized position by photoconductor 44 which is independently connected to the voltage supply source. The darkening of lamp 12 removes the hold-off shunt circuit across lamp 10 provided by photo-conductor 53. The removal of the shunt across lamp 10 provided by the hold-off photoconductor 58 would be expected to cause lamp it? to be energized through condition photoconductor 48 illuminated by lamp 1 1. However, the condition power supply circuit St) is grounded by the illumination of photoconductor 52 from trigger lamp 26. Accordingly, main lamp it remains dark as long as trigger lamp 26 is illuminated. However, at the end of the trigger pulse, when lamp 26 is extinguished, the voltage of the condition circuit 59 rises, and main lamp 19 is then energized. The latch supply circuit 40 also rises in voltage so that lamp 110 latches itself on through latching photoconductor 32. Main lamp 12 is not relighted because, with conditioning lamp in off,

there is no active energizing circuit for that lamp once the latching circuit through photoconductor 34 becomes inactive.

Once lamp in is illuminated and latched on, the shunt photoconductor 5'3 extinguishes the conditioning lamp 214, and the pick-up photoconductor 60 causes energization of conditioning lamp 16. The resultant illumination of condition photoconductor 49 would then cause energization of main lamp 12, except that hold-off photoconductor 56, which is illuminated by main lamp 10, prevents such energization. Photoconductor 30, of course, provides an output B at connection 20.

It will be seen that the connections of the main lamp 1% and the conditioning lamp 14 are symmetrical with the connections of main lamp 12 and conditioning lamp 16, and their associated photoconductors. Accordingly, it is apparent by analogy that when the next trigger pulse is applied to trigger lamp 26, a similar shift from main lamp 110 back to main lamp 12 will occur. Thus, whenever a trigger pulse is received to illuminate trigger lamp 126, a change in the circuit from one stable state to the other will occur.

if a signal is received by a reset lamp 24, the resultant voltage supplied through photoconductor 68 to lamp 1%, and the resultant shunt circuit provided by a photoconductor 70 for lamp 12 will assure that the circuit will either achieve, or remain in, the state in which lamp 1!) is illuminated and lamp 12 is extinguished. This is the condition opposite to that achieved by a ct input on lamp 22.

FIG. 2 is a schematic diagram of a reversible ring circuit embodiment of the present inventionillustrating how more than two stable states may be accommodated in a ring or commutator circuit. The embodiment of FIG. 2 shows three stages of a multiple state circuit which may be extended to have any desired number of stages so as to be capable of achieving any one of a corresponding number of dilferent states. The components of each stage have been lettered to correspond to the ettering of certain analogous components in FIG. 1.

Thus, for the first stage there is a main lamp 18A corresponding to main lamp 19 in FIG. 1 and a conditioning lamp 14A corresponding to conditioning lamp 14 of PEG. 1. The associated photoeonductors are similarly lettered for the first stage with the sul'fix A. The corresponding parts for the other stages are similarly lettered, but with the sutiix B for the second stage and with the sufiix C for the third stage. Instead of the bistable or two state back and forth shifting operation of FIG. 1, the system of FIG. 2 provides for shifting successsively either to the right or to the left. Accordingly, lamp 26A is characterized as an advance lamp rather than a trigger. Further, the piclnup photoconductor 60A provides for energizaticn of condition lamp 148 for a right shift operation and similarly, the pick-up photoconductor 6013 provides for encrgization of condition lamp 14C for a continuing right shift operation. All of the right shift pick-up photoconductors 60A, 60B, 69C, etc. are energized from a right shift bus 72 which is supplied through an energizing photoconductor 74 under the control of a right shift control lamp 76.

If a reversible ring is required, a corresponding left sift bus 78 ,is provided which is similarly energizable through a photoconductor 80 under the control of a left shift lamp 82. Individual left shift pick-up photoconductors are provided at each stage of the ring, as indicated at 84A, 84B, and 34C, each of which is energized from the left shift bus 7 8. Each of these photoconductors is connected to energize the conditioning lamp for the next stage to the left of the stage with which it is associated. To complete the apparatus necessary for the left shift controls, an additional holdoff photoconductor must be provided for each stage, as indicated at 86A, 86B, and 36C, which is connected in shunt with the main lamp of the next stage to the left. These are the exact counterparts of the right shift hold-off photoconductors 56A, 56B, and 56C.

In order to reset the ring and to drop any information which is stored in the ring, a turn off lamp 855 is provided having associated photoconductors 9t 92, and 94 which provide shunt circuits for all of the latching power supply circuits so that any main or conditioning lamp which is latched on is dropped out and extinguished. Thus, photoconductor M is in shunt with the main lamp latching but 46A and photoconductors 90 and '92 are in shunt with the conditioning lamp voltage supply buses indicated at 96 and 98. The latching circuits for the conditioning lamps of the various ring stages are alternately connected to buses 96 and 93.

The operation of the system of FIG. 2 is quite analogous to the operation previously described for the system of FIG. 1. When operation is to commence, the turn off lamp 83 may be pulsed to drop out any information stored in the ring by extinguishing any lamps which are latched on. Then, one of the start lamps 24A, 242, or 24C is given a pulse depending on which ring position is to be started with. If start lamp Z E-A is pulsed to energize the first ring position, then voltage is supplied through photoconductor 68A to cause illumination of main lamp 10A which latches itself in the illuminated position through photoconductor 32A. Then, for right shift operation, the right shift lamp 76 is illuminated and power is thus supplied to the right shift bus 72 through photoconductor 74. This energizes conditioning lamp 143 through pick-up photoconductor 60A. When an advance is to occur, the advance lamp 26A is pulsed, which turns off main lamp 10A and disables the condition bus 56A. However, conditioning lamp 14B remains latched on. Accordingly, at the end of the advance pulse when the advance lamp ZdA is extinguished, the conditioning but 50A is again eifective and the resultant power supplied through condition photoconductor 48B picks up and illuminates main lamp 1GB. Lamp lilB then causes conditioning lamp 14C to come on through pick-up photoconductor 69B, and shuts off conditioning lamp 14B through the shunt circuit provided by photoconductor 5313. Thus, a shift of one stage to the right is accomplished. With the next advance pulse, a similar shift to the third stage is accomplished.

If it is then decided to change to left shift operation, the right shift lamp 76 is extinguished, and the left shift lamp 82 is illuminated. The pick-up photoconductor 84C is then elfective to pickup conditioning lamp 14B, and an advance pulse then causes a shift to the left from the third stage to the second stage. Depending on which main lamp is illuminated, an output is always indicated at one of theoutput connections 20A, 2913, or ZtlC.

It is generally contemplated that a ring circuit constructed in accordance with FIG. 2 will have many more than three stages, but only three typical stages are shown in order to simplify the illustration of the invention. It will thus be understood that additional stages may be provided by simply duplicating and repeating the structure of the stages which are shown. it is apparent also that the ring, as illustrated in FIG. 2, and as expanded to the desired length, may be connected for recirculatory operation, if desired. This may be done by appropriately interconnecting the outgoing connections from the last stage, as indicated at 'llllti through. M6, to the corresponding outgoing connections of the first stage, as indicated at 108 through 114.

While FIG. 2 illustates a reversible ring circuit, if it is necessary only to provide for shifting in one direction, then the circuit components and connections employed in shifting in the other direction may be omitted. For instance, if the circuit in FIG. 2 is only to shift to the right, the left shift pick-up photoconductors 84A, 84B, and 84C may be omitted and the hold-oif photoconductors 86A, 86B, and 860 may be omitted. 1

The similarities between the embodiments of FIGS. 1'.

and 2 may be emphasized by the following observation. If the system of FIG. 2 is arranged for shifting in only one direction, as described just above, and reduced to only two stages, and connected for recirculation, then it will be very similar to the bi-stable system of FIG. 1.

As previously mentioned above, although the term photoconductor is used to describe each of the responsive devices employed in the preferred embodiments of the present invention, it should be emphasized that each of these devices are more accurately described as impedanccs which achieve a substantially reduced impedance value when they are illuminated. Thus it is contemplated that the impedance of one of these devices may be at least in the order of 200 megohms when not illuminated. But, when it is subjected to illumination its resistance may drop to a typical value in the order of 50,000 ohms and very seldom will the illuminated impedance go below a value of 10,000 ohms. Thus, it is to be seen that a device having a minimum resistance of thousands of ohms, although commonly referred to as a photoconductor, should be more accurately described as an impedance having photoresponsive properties. How ever, the term photoconductor and the like is used in this specification, keeping these qualifications in mind. in the description of the circuits, for convenience, circuit paths areoften described as completed by the illumination of a particular photoconductor. It will be understood that this is not strictly correct because such a statement really means that a circuit path of lowered impedance is created by illumination of a photoconductor in a circuit which already exists.

Photoconductive devices having impedance characteristics as described above are commercially available. For instance, one such device may be purchased from the Clairex Corporation, of 50 West 26th Street, in New York City, under model number CL3A.

The typical impedance of the photoconductor as indicated above, $350,000 ohms when illuminated, is up licable when the illumination is from a neon glow lamp positioned within reasonable proximity to the photoconductor, Small, inexpensive neon glow lamps which are suitable for this purpose are commonly available. A typical device of this kind is available for instance from the General Electric Company under Model No. NE-Z. Such a device may require about "70 volts to initiate glow conduction when new, but after appreciable aging has occurred, the firing voltage may advance to the order of 115 volts. After the lamp has become illuminated, a negative resistance effect is to be observed such that the voltage across the glow lamp may drop to about 55 volts. As the lamp ages, this voltage also rises to a maximum value in the order of volts. The current required for such a neon lamp may vary from one quarter of a milliarnpere to one milliarnpere.

It will be appreciated that various other voltage responsive light source devices may be employed and that other photoresponsive devices may be used to detect the illumination from such devices. For instance, the voltage responsive light sources may be electroluminescent devices, or incandescent filament devices, or devices employing gaseous discharges to derive illumination from fluorescent coatings. In each instance, photoconductive devices are selected which are particularly responsive to the spectrum of light emitted by the light source employed. Fortunately, the neon lamps mentioned above and the. photoconductivedevices mentioned above work well together. Accordingly, the neons are preferred and the light sources in the present specification are all indicated as being neon light sources, but it will be understood that other sources may be employed if desired.

One important advantage of the neon glow lamp as an electrical voltage responsive light source in the present system is the fact that it remains substantially completely dark until its firing voltage threshold is achieved,. at which time it suddenly provides a substantially full output illumination with a reduced voltage requirement. This characteristic is very desirable because it prevents false operation as long as the voltage is below the threshold value. It also provides for positive operation whenever the voltage goes above the threshold.

With neon glow lamps, it is generally necessary that some series impedance be employed, as well as some shunt impedance. The value of each of the shunt impedances is preferably about one megohm. This one megohm shunt across each neon serves to set a maximum impedance for the neon with respect to the remainder of the circuit. Although impedance values for the various circuit components are not specified, it will be understood that whenever operation is required to provide output illumination, the series impedances for the various neons generally will be so chosen as to result in a neon current in the order of one milliampere.

In order to simplify the drawings and make them clearer and more easily understood some of the lamp shunt impedances are omitted from the drawings, out it will be understood that such impedances are to be employed in the practical embodiments of the invention. Also, to further simplify the drawings, the power supply connections are not wired in, either at the common ground connection or at the high voltage connections. The common ground connections are indicated conventionally by the ground symbol, and the high voltage connections are indicated by a terminal symbol with a sign. The value of the supply voltage may be selected to conform to the impedance value and the current requirements of the circuit design. A good workable value of supply voltage has been found to be about 300 volts. When employing neon lamps as the light sources, it has been found desirable to employ a direct current power supply source, or an alternating current power supply at a frequency of about 1000 cycles. With other light sources, other voltages and frequencies may be employed. Conventional sources of power may be employed to obtain satisfactory operation of the systems of the present invention.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A multi-state photologic circuit comprising a main voltage responsive light source for each state, a conditioning voltage responsive light source associated with each main light source, each of said light sources having a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when once illuminated, each main light source having photoconductors arranged to receive illumination therefrom including a shut-off photoconductor connected in shunt with the associated conditioning light source and a photoconductor connected in shunt with the last preceding main light source actuated and a pick-up photoconductor connected to supply a pick-up voltage to the conditioning light source for the next succeeding main light source to be actuated, switching means operable to turn off any illuminated main light source whenever a shift in state is required, and circuit means including a condition photoconductor associated with each conditioning light source for turning of the next main light source.

2. A two-state photologic circuit comprising a main voltage responsive light source for each state, a conditioning voltage responsive light source associated with each main light source, each of said light sources having a latching photoconductor arranged for illuminationthereby and connected to supply a maintaining voltage thereto when once illuminated, a se light source and photoconductors arranged for illumination thereby and respectively connected to energize the first of said main light sources and to shunt the second of said main light sources,

a reset light source and photoconductors arranged for illumination thereby and respectively connected to energize the second of said main light sources and to shunt the first of said main light sources, each main light source having photoconductors arranged to receive illumination therefrom including a shut-off photoconductor connected in shunt with the associated conditioning light source and a pick-up photoconductor connected to supply a pick-up voltage to the conditioning light source for the other main light source, switching means operable to turn off the illuminated main light source whenever a shift in state is required, and circuit means including a condition photoconductor associated with each conditioning light source for turning on the other main light source.

3. A multi-state photologic circuit comprising a main self-latching voltage responsive light source for each state, a photoconductor arranged for illumination by said main light source for connecting voltage to said light source for latching it on, a conditioning device for each of said main light sources, each of said conditioning devices comprising a second voltage responsive light source and a photoconductor arranged for illumination thereby for latching said second light source on when once illuminated, said conditioning device including a second photoconductor arranged for illumination by said conditioning light source and connected to supply a voltage to the associated main light source, a second photoconductor associated with each main light source and arranged for illumination thereby and connected to supply a pick-up voltage to the conditioning device for the next succeeding main light source to be actuated, a third photoconductor associated with each main light source and arranged to receive illumination therefrom connected in shunt with the associated conditioning light source for extinguishment thereof, a fourth photoconductor associated with each light source and arranged for illumination thereby and connected in shunt with the next succeeding main light source to maintain said succeeding main light source in the non-illuminated condition, all of said latching photo conductors for said main light sources being connected for energization from a common supply voltage source, a triggering signal device for reducing the voltage of said common latching voltage supply connection to extinguish any illuminated main light source whenever a change in the state of the system is required, and an output photoconductor arranged to receive illumination from at least one of said main light sources.

4. A multi-state photologic circuit comprising a main voltage responsive light source for each state, a conditioning voltage responsive light source associated with each main light source, each of said light sources having a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when the light source is once illuminated, each conditioning light source having associated therewith a conditioning photoconductor arranged for illumination thereby and connected to supply a voltage to the associated main light source, each main light source having the following photoconductors associated therewith and arranged to receive illumination therefrom: a shut-off photoconductor connected in shunt with the associated conditioning light source for shutting off said conditioning light source and a pick-up photoconductor connected to supply a pick-up voltage to the conditioning light source for the next succeeding main light source to be actuated and a hold-off photoconductor connected in shunt with the next succeeding main light source to be actuated to prevent such actuation as long as the hold-01f photoconductor is illuminated, said latching photoconductors for said main light sources being connected in a common circuit to a source of energizing voltage, a photoconductive trigger device connected to said common circuit for changing the voltage level thereof whenever a change in state is required, and an output photoconductor arranged to receive illumination from at least one of said light sources.

5. A multi-state photologic circuit comprising a main lamp for each state, a conditioning lamp associated with each main lamp, each of said lamps having a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when the lamp is once illuminated, each conditioning lamp having a condition photoconductor arranged for illumination thereby and connected to supply a voltage to the associated main lamp, said condition photoconductors being connected to an energizing voltage through a common condition supply circuit, each main lamp having the following photoconductors arranged to receive illumination therefrom; a shut-oil photoconductor connected in shunt with the associated conditioning lamp and a pick-up photoconductor connected to supply a pick-up voltage to the conditioning light source for the next succeeding main lamp to be actuated and a hold-01f photoconductor connected in shunt with the next succeeding main light source to be actuated, said latching photoconductors for said main lamps being connected in a common latch supply circuit to a source of energizing voltage, an advance lamp arranged to be illuminated whenever a change in state is required, two photoconducto-rs arranged to receive illumination from said advance lamp and respectively connected to ground said common condition supply and latch supply circuits, and an output photoconductor arranged to receive illumination from at least one of said main and conditioning lamps.

6. A multi-state reversible photologic ring circuit comprising a main lamp for each state, a starting lamp for each state, each starting lamp having a photoconductor arranged for illumination thereby and connected to energize the associated main lamp, a conditioning lamp associated with each main lamp, each of said main and conditioning lamps having a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when the lamp is once illuminated, each conditioning lamp having a condition photoconductor arranged for illumination thereby and connected to supply a voltage to the associated main lamp, each main lamp having the following photoconductors arranged to receive illumination therefrom; a shut-off photoconductor connected in shunt with the associated conditioning lamp and a right shift pick-up photoconductor and a left shift pick-up photoconductor and right and left shift hold-01f photoconductors respectively connected in shunt with the next succeeding main lamp-s to the right and to the left, all of said night shift pick-up photoconductors being connected in a common right shift power supply circuit to be energized in response to a right shift signal and all of said left shift pick-up photoconductors being connected in a common left shift power supply circuit to be energized in response to a left shift signal, said condition photoconductors being connected to a source of energizing voltage through a common condition supply circuit, said latching photoconductors for said main lamps being connected to a source of energizing voltage through a common latch supply circuit, an advance lamp arranged to be illuminated whenever a change in state is required, two photoconductors arranged to receive illumination from said advance lamp and respectively connected to ground said common condition supply and latch supply circuits, and an output photoconductor arranged to receive illumination from at least one of said main and conditioning lamps.

7. A multi-state reversible photologic ring circuit comprising a main lamp for each state, a starting lamp for each state, each starting lamp having a photoconductor arranged for illumination thereby and connected to energize the associated main lamp, a conditioning lamp associated with each main lamp, each of said main and contioning lamps having a latching photoconductor arranged for illumination thereby and connected to supply a maintaining voltage thereto when the lamp is once illuminated, each conditioning lamp having a condition photoconductor arranged for illumination thereby and connected to supply a voltage to the associated main lamp, each main lamp having the following photoconductors arranged to receive illumination therefnorn; a shut-off photoconductor connected in shunt with the associated conditioning lamp and a right shift pick-up photoconductor and a left shift pickup photoconductor and right and left shift hold-off photoconductors respectively connected in shunt with the next succeeding main lamps to the right and to the left, all of said right shift pick-up photoconductors being connected in a common right shift power supply circuit comprising a photoconductor and operable in response to an optical illumination right shift signal thereon and all of said left shift pick-up photoconductors being connected in a common left shift power supply circuit comprising a photocond-uctor and operable in response to an optical illumination left shift signal thereon, said condition photoconductors being connected to a source of energizing voltage through a common condition supply circuit, said latching photoconductors for said main lamps being connected to a source of energizing voltage through a common latch supply circuit, an advance lamp arranged to be illuminated whenever a change in state is required, two photoconductors arranged to receive illumination from said advance lamp and respectively connected to gr'ound said.

common condition supply and latch supply circuits, an

output photoconductor arranged to receive illumination from at least one of said main and conditioning lamps, and a turn-off lamp having photoconductors arranged to receive illumination therefrom and connected to shunt the supply voltage to each of said main and conditioning lamp latching photoconductor circuits.

References Cited in the file of this patent UNITED STATES PATENTS 2,727,683 Allen et al Dec. 20, 1955 2,949,538 Tomlinson Aug. 16, 1960 2,985,763 Ress May 23, 1961 2,997,596 Vize Aug. 22, 1961 3,020,410 Bowerman Feb. 6, 1962 

6. A MULTI-STATE REVERSIBLE PHOTOLOGIC RING CIRCUIT COMPRISING A MAIN LAMP FOR EACH STATE, A STARTING LAMP FOR EACH STATE, EACH STARTING LAMP HAVING A PHOTOCONDUCTOR ARRANGED FOR ILLUMINATION THEREBY AND CONNECTED TO ENERGIZE THE ASSOCIATED MAIN LAMP, A CONDITIONING LAMP ASSOCIATED WITH EACH MAIN LAMP, EACH OF SAID MAIN AND CONDITIONING LAMPS HAVING A LATCHING PHOTOCONDUCTOR ARRANGED FOR ILLUMINATION THEREBY AND CONNECTED TO SUPPLY A MAINTAINING VOLTAGE THERETO WHEN THE LAMP IS ONCE ILLUMINATED, EACH CONDITIONING LAMP HAVING A CONDITION PHOTOCONDUCTOR ARRANGED FOR ILLUMINATION THEREBY AND CONNECTED TO SUPPLY A VOLTAGE TO THE ASSOCIATED MAIN LAMP, EACH MAIN LAMP HAVING THE FOLLOWING PHOTOCONDUCTORS ARRANGED TO RECEIVE ILLUMINATION THEREFROM; A SHUT-OFF PHOTOCONDUCTOR CONNECTED IN SHUNT WITH THE ASSOCIATED CONDITIONING LAMP AND A RIGHT SHIFT PICK-UP PHOTOCONDUCTOR AND A LEFT SHIFT PICK-UP PHOTOCONDUCTOR AND RIGHT AND LEFT SHIFT HOLD-OFF PHOTOCONDUCTORS RESPECTIVELY CONNECTED IN SHUNT WITH THE NEXT SUCCEEDING MAIN LAMPS TO THE RIGHT AND TO THE LEFT, ALL OF SAID RIGHT SHIFT PICK-UP PHOTOCONDUCTORS BEING CONNECTED IN A COMMON RIGHT SHIFT POWER SUPPLY CIRCUIT TO BE ENERGIZED IN RESPONSE TO A RIGHT SHIFT SIGNAL AND ALL OF SAID LEFT SHIFT PICK-UP PHOTOCONDUCTORS BEING CONNECTED IN A COMMON LEFT SHIFT POWER SUPPLY CIRCUIT TO BE ENERGIZED IN RESPONSE TO A LEFT SHIFT SIGNAL, SAID CONDITION PHOTOCONDUCTORS BEING CONNECTED TO A SOURCE OF ENERGIZING VOLTAGE THROUGH A COMMON CONDITION SUPPLY CIRCUIT, SAID LATCHING PHOTOCONDUCTORS FOR SAID MAIN LAMPS BEING CONNECTED TO A SOURCE OF ENERGIZING VOLTAGE THROUGH A COMMON LATCH SUPPLY CIRCUIT, AN ADVANCE LAMP ARRANGED TO BE ILLUMINATED WHENEVER A CHANGE IN STATE IS REQUIRED, TWO PHOTOCONDUCTORS ARRANGED TO RECEIVE ILLUMINATION FROM SAID ADVANCE LAMP AND RESPECTIVELY CONNECTED TO GROUND SAID COMMON CONDITION SUPPLY AND LATCH SUPPLY CIRCUITS, AND AN OUTPUT PHOTOCONDUCTOR ARRANGED TO RECEIVE ILLUMINATION FROM AT LEAST ONE OF SAID MAIN AND CONDITIONING LAMPS. 